A difficult problem for the studies of amine uptake by nerve endings in peripheral organs is the small proportion of tissue that actually participates in the uptake phenomenon. For example, slices of rat ventricle contain less than 0.1% of adrenergic nerve endings. Hence, even poor uptake by the large bulk of muscle tissue affects the results of uptake studies. Conversely, if the concentration of amine in heart reached equality with that in the extra-cellular fluid, then the uptake into nerve tissue would be at least 1000:1 to raise the overall tissue concentration to 2:1. To increase the precision of uptake studies using heart slices, some estimate of the uptake by non-carrier mediated uptake in the tissue is required to estimate uptake by carrier-mediated mechanisms in neuronal tissue. We have been using a tissue medium ratio of 0.8 as an adjustment factor for this purpose. More data is now available and the problem was re-investigated for current studies.